Surface Structure Modulation Of Non-noble Metal Catalysts And Their Application In Carbon Dioxide Photo/Electroreduction

Excessive consumption of fossil energy not only accelerates the arrival of the energy crisis,but also causes serious environmental problems such as global warming.Converting excess carbon dioxide(CO2)in the atmosphere into value-added carboncontaining fuels through photocatalysis or electrocatalysis is an effective way to solve these two critical problems at the same time.Unfortunately,limited by the molecular inertness of CO2 and the complexity of the reaction process,the efficiency of CO2 reduction reaction and the selectivity of specific products are still unsatisfactory.Because the reduction of CO2 often occurs on the surface of the catalyst,adjusting the surface structure of the catalyst can directly affect the reaction process of CO2 reduction,realizing precise control of the reaction activity and product selectivity.In view of this,a wide range of inexpensive non-precious metal materials were selected as catalysts toobtain different CO2 reduction products with high selectivity.The surface structures of related catalysts were regulated by means of defects,doping and morphology control,which successfully improve the reactivity and product selectivity of the CO2 reduction reaction.In addition,we also use a variety of in situ characterization methods and theoretical simulation calculations to conduct in-depth analysis of the key steps during the catalytic process,which reveals some key factors that influence the catalytic performance.The main contents of this dissertation are as follows:1.Atmospheric CO2 capture and photofixation to near-unity CO by Ti3+-VoTi3+sites confined in TiO2 ultrathin layers:To realize efficient atmospheric CO2 chemisorption and activation,abundant Ti3+sites and oxygen vacancies in TiO2 ultrathin layers were designed.Positron annihilation lifetime spectroscopy and theoretical calculations first unveil each oxygen vacancy is associated with the formation of two Ti3+sites,giving a Ti3+-Vo-Ti3+configuration.The Ti3+-Vo-Ti3+sites could bond with CO2 molecules to form a stable configuration,which converted the endoergic chemisorption step to an exoergic process,verified by in-situ Fouriertransform infrared spectra and theoretical calculations.Also,the adjacent Ti3+sites not only favor CO2 activation into COOH-via forming a stable Ti3+-C-O-Ti3+configuration,but also facilitate the rate-limiting COOH-scission to CO-by reducing the energy barrier from 0.75 to 0.45 eV.Thus,the Ti3+-Vo-TiO2 ultrathinlayers could directly capture and photofix atmospheric CO2 into near-unity CO,with the corresponding CO2-to-CO conversion ratio of ca.20.2%.2.Ultrathin Ti-doped WO3 Nanosheets Realizing Selective Photoreduction of CO2 to CH3OH:Compared with the previous CO,the multi-electron reduction product CH3OH has higher energy density and broader industrial application prospects.However,arduous CO2 activation and sluggish charge transfer retard the CO2 photoreduction to CH3OH with high efficiency and selectivity.Here,we fabricate ultrathin Ti-doped WO3 nanosheets possessing approving active sties and optimized carrier dynamics as a promising catalyst.Quasi in situ X-ray photoelectron spectroscopy and synchrotron-radiation X-ray absorption near-edge spectroscopy firmly confirm that the true active sites for CO2 reduction are the W sites rather the Ti sites,while the Ti dopants can facilitate the charge transfer,which accelerates the generation of crucial COOH*intermediates as revealed by in situ Fourier-transform infrared spectroscopy and density functional theory calculations.Besides,the Gibbs free energy calculations also validate that Ti doping can lower the energy barrier of CO2 activation and CH3OH desorption by 0.22 eV and 0.42 eV,respectively,thus promoting the formation of CH3OH.In consequence,the Ti-doped WO3 ultrathin nanosheets show a superior CH3OH selectivity of 88.9%and reach a CH3OH evolution rate of 16.8 μmol g-1h-1,about 3.3 times higher than that on the WO3 nanosheets.3.Surface Engineering on Commercial Cu Foil for Steering C2H4/CH4 Ratio in CO2 Electroreduction:Compared with the preparation of the above Ci products,conversion of CO2 to C2+products with high selectivity is more difficult and challenging.So far,electrocatalysis is the most efficient way to generate C2+products.Therefore,in order to design the corresponding high-efficiency electrocatalyst,we propose a Cu foil kinetic model with abundant nanocavities possessing higher reaction rate constant k to steer the ratio of C2H4 to the competing CH4 during CO2 electroreduction.Chemical kinetic simulation manifested that the nanocavities could enrich the adsorbed CO surface concentration(θCOad),while the higher k helps to lower the C-C coupling barrier for CO intermediates,thus favoring the formation of C2H4.The commercial Cu foil treated with cyclic voltammetry is used to match this model,displaying a remarkable C2H4/CH4 ratio of 4.11,which is 18 times larger than that on the pristine Cu foil.